Current commercial ophthalmic lenses are produced from glass, allylcarbonate thermoset (thermosetting polycarbonate) or thermoplastic aromatic polycarbonate. Their relatively low weight and durability make the later materials desirable for the manufacture of ophthalmic lenses. The use of thermoplastic aromatic polycarbonate in this market has been increasing annually mainly because glass and thermosetting polycarbonate are inferior to thermoplastic aromatic polycarbonate in terms of impact resistance. Thermoplastic aromatic polycarbonate is therefore rapidly replacing both of these materials.
While current thermoplastic aromatic polycarbonate can closely match the performance of glass and thermosetting polycarbonate in almost every aspect, its photochromic behavior falls short of expectations. The incorporation of photochromic dyes into a thermoplastic aromatic polycarbonate (herein "PC") matrix is problematic. First, photochromic dyes in an unmodified PC matrix show slow transition between the light and dark forms. This slow transition rate makes the photochromic material less competitive with the glass and allylcarbonate thermoset photochromic lenses, which are presently commercially available. Second, the glass transition temperature of PC is relatively high and photochromic dyes are thermally sensitive. Hence, during the injection molding process, there is a distinct possibility that the dyes will degrade and shift the color of the corresponding lenses to a more yellow tint. The resulting color is generally unacceptable to the optical lens industry.
These shortcomings of thermoplastic aromatic polycarbonate in terms of photochromicity are perceived as a hindrance to wider acceptance of the material in this industry. Therefore, workers in the field have been attempting to produce a viable and economical thermoplastic aromatic polycarbonate lens having photochromic properties.
Methods for producing plastic lenses are known. U.S. Pat. No. 5,496,641 disclosed a plastic lens, the structure of which included a substrate of a particular refractive index, a primer layer comprising a metal compound, a hard coating layer and an anti-reflection layer.
U.S. Pat. No. 5,531,940 disclosed a method which entails providing (a) a finished or semifinished plastic lens preform having a first convex surface that is spherical or aspherical in geometry, (b) a mold having a molding surface at least a portion of which has a profile substantially matching the convex surface of the preform and (c) an uncured resin having a low crosslinking density and forms a soft matrix upon curing. These are arranged such that the uncured resin is disposed between convex surface of the preform and the molding surface of the mold, the composite plastic lens is impregnated with a photochromic material. In an additional embodiment of the '940 patent, the method entails using as (c) a photochromic-additive-containing uncured resin. In a still additional embodiment, the '940 patent disclosed a second uncured resin having a relatively high crosslinking density, which forms a scratch resistant matrix upon curing. Also disclosed is the method where the first uncured resin that has a low crosslinking density includes a photochromic additive. Polycarbonate is among the preferred materials for making the lens preform. A related method has been disclosed in PCT WO 95/15845. Also, presently practiced technology for manufacturing photochromic PC ophthalmic lens entails first cleaning a molded lens and then attaching a polyurethane film to one of the lens surfaces. To the outside surface of the polyurethane film there is then applied a second film, such as polyester, which contains appropriate photochromic dyes to form a combination through a thermal treatment of the combination, the photochromic dye diffuses, or migrates from the second film into the polyurethane film. The second film is then removed and the polyurethane surface is hard-coated to produce the final product. The resulting, now photochromic, combination is then used to make a lens. The process is economically unattractive and is characterized by its relatively low yield. Moreover, certain lenses, such as bifocals and progressives, cannot currently be produced by this method. On the other hand, it is important to have the dye on the outside surface of the lens most efficient in terms of activating the photochromic dye and only minimum amounts of the dyes are required to produce this photochromic lens. Moreover, in contrast to the thermal degradation which is often the consequence of having the photochromic dyes dispersed in the bulk material, thermal instability is not an issue because the dyes are transferred to the lenses at a relative low temperature.
The relevant art also includes U.S. Pat. No. 3,567,605 that disclosed a series of pyran and chromene derivatives that have been reported to undergo color change on exposure to radiation. Also relevant are U.S. Pat. Nos. 5,451,344 and 5,552,090 that disclosed the photochromic naphthopyrans, which are useful in the present invention. The '090 document disclosed the utility of such compounds in the preparation of photochromic articles molded of any polymeric resins including thermoplastic polycarbonate resins. Also relevant is U.S. Pat. No. 4,064,195 that disclosed a molding composition containing polycarbonate (PC) and polycaprolactone polymer (PCL).
A key object of the present invention is to provide a film having photochromic properties suitable for the manufacture of photochromic lenses.
An additional object is to provide a method for making a photochromic lens using the inventive film.